U.S. patent number 11,316,168 [Application Number 16/331,024] was granted by the patent office on 2022-04-26 for flexible secondary battery.
This patent grant is currently assigned to LG Energy Solution, Ltd.. The grantee listed for this patent is LG Energy Solution, Ltd.. Invention is credited to Sung-Joong Kang, Dong-Chan Lee, Jae-Hyun Lee, In-Sung Uhm.
United States Patent |
11,316,168 |
Lee , et al. |
April 26, 2022 |
Flexible secondary battery
Abstract
A flexible secondary battery includes: a first electrode
including a first electrode current collector extended
longitudinally, a first electrode active material layer formed on
the outside of the first electrode current collector, and a first
insulation coating layer formed on the outside of the first
electrode active material layer; and a second electrode including a
second electrode current collector extended longitudinally, a
second electrode active material layer formed on the outside of the
second electrode current collector, and a second insulation coating
layer formed on the outside of the second electrode active material
layer, wherein the first electrode and the second electrode are
wound in such a manner that they are disposed alternately in
contact with each other.
Inventors: |
Lee; Jae-Hyun (Daejeon,
KR), Uhm; In-Sung (Daejeon, KR), Kang;
Sung-Joong (Daejeon, KR), Lee; Dong-Chan
(Daejeon, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
LG Energy Solution, Ltd. |
Seoul |
N/A |
KR |
|
|
Assignee: |
LG Energy Solution, Ltd.
(N/A)
|
Family
ID: |
1000006265009 |
Appl.
No.: |
16/331,024 |
Filed: |
December 11, 2017 |
PCT
Filed: |
December 11, 2017 |
PCT No.: |
PCT/KR2017/014489 |
371(c)(1),(2),(4) Date: |
March 06, 2019 |
PCT
Pub. No.: |
WO2018/106093 |
PCT
Pub. Date: |
June 14, 2018 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190267633 A1 |
Aug 29, 2019 |
|
Foreign Application Priority Data
|
|
|
|
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Dec 9, 2016 [KR] |
|
|
10-2016-0167907 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M
10/0587 (20130101); H01M 4/78 (20130101); H01M
4/628 (20130101); H01M 4/366 (20130101); H01M
2004/025 (20130101); H01M 4/02 (20130101); H01M
4/13 (20130101) |
Current International
Class: |
H01M
4/00 (20060101); H01M 10/0587 (20100101); H01M
4/78 (20060101); H01M 4/36 (20060101); H01M
4/62 (20060101); H01M 4/13 (20100101); H01M
4/02 (20060101) |
References Cited
[Referenced By]
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Other References
Machine Translation of WO-2014021691-A1 (Year: 2014). cited by
examiner .
Extended European Search Report for Application No. EP17877575.5
dated Sep. 25, 2019, pp. 1-3. cited by applicant .
Search report from International Application No. PCT/KR2017/014489,
dated Apr. 11, 2018. cited by applicant .
Chinese Search Report for Application No. 201780065285.9 dated Sep.
8, 2021, 3 pages. cited by applicant.
|
Primary Examiner: Cano; Milton I
Assistant Examiner: Henshaw; Mary G
Attorney, Agent or Firm: Lerner, David, Littenberg, Krumholz
& Mentlik, LLP
Claims
What is claimed is:
1. A flexible secondary battery comprising: a first electrode
comprising a first electrode current collector extended
longitudinally, a first electrode active material layer formed on
an outside of the first electrode current collector, and a first
insulation coating layer formed on an outside of the first
electrode active material layer; and a second electrode comprising
a second electrode current collector extended longitudinally, a
second electrode active material layer formed on an outside of the
second electrode current collector, and a second insulation coating
layer formed on an outside of the second electrode active material
layer, wherein the first electrode and the second electrode are
helically wound in contact with each other such that they are
disposed alternately in parallel with each other on the same
circumference, wherein the flexible secondary battery further
comprises a third insulation coating layer completely surrounding
outside surfaces of both the first electrode and the second
electrode and wherein the third insulation coating layer is a
helically wound structure in contact with the first electrode and
the second electrode so that the first electrode and the second
electrode are not spaced apart from each other even under
continuous bending of the secondary battery and are maintained as
one pair at an originally aligned position, wherein each of the
first insulation coating layer, the second insulation coating
layer, and the third insulation coating layer comprises a
polyolefin foam separator.
2. The flexible secondary battery according to claim 1, wherein
each of the first electrode current collector and the second
electrode current collector independently comprises: stainless
steel; aluminum; nickel; titanium; baked carbon; copper; stainless
steel surface-treated with carbon, nickel, titanium or silver;
aluminum-cadmium alloy; non-conductive polymer surface-treated with
a conductive material; conductive polymer; metal paste containing
metal powder of Ni, Al, Au, Ag, Al, Pd/Ag, Cr, Ta, Cu, Ba or ITO;
or carbon paste containing carbon powder of graphite, carbon black
or carbon nanotube.
3. The flexible secondary battery according to claim 1, wherein the
first electrode is a cathode or anode and the second electrode is
an anode or cathode corresponding to the first electrode.
4. The flexible secondary battery according to claim 1, wherein
when the first electrode is an anode and the second electrode is a
cathode, the first electrode active material comprises any one
active material particle selected from the group consisting of
natural graphite, artificial graphite or carbonaceous materials;
metals (Me) of lithium-containing titanium composite oxide (LTO),
Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; alloys including the metal
(Me); oxides (MeOx) of the metals (Me); and composites of the
metals (Me) with carbon, or a combination of two or more of them,
and the second electrode active material comprises any one active
material particle selected from the group consisting of
LiCoO.sub.2, LiNiO.sub.2, LiMn.sub.2O.sub.4, LiCoPO.sub.4,
LiFePO.sub.4, LiNiMnCoO.sub.2 and LiNi.sub.1-x-y-z
Co.sub.xM1.sub.yM2.sub.zO.sub.2 (wherein each of M1 and M2
independently represents any one selected from the group consisting
of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, each of x, y
and z independently represents the atomic fraction of an element
forming the oxide and 0.ltoreq.x<0.5, 0.ltoreq.y<0.5,
0.ltoreq.z<0.5 and 0<x+y+z.ltoreq.1), or a combination of two
or more of them.
5. The flexible secondary battery according to claim 1, wherein a
cross-section of the third insulation coating layer is an
elliptical shape or a rectangular shape.
6. The flexible secondary battery according to claim 1, wherein
each of the first electrode current collector and the second
electrode current collector independently comprises non-conductive
polymer surface-treated with a conductive material.
7. The flexible secondary battery according to claim 6, wherein the
conductive material is selected from the group consisting of
polyacetylene, polyaniline, polypyrrole, polythiophene, polysulfur
nitride, indium tin oxide (ITO), copper, silver, palladium and
nickel.
8. The flexible secondary battery according to claim 1, wherein
each of the first electrode current collector and the second
electrode current collector independently comprises conductive
polymer.
9. The flexible secondary battery according to claim 8, wherein the
conductive polymer is selected from the group consisting of
polyacetylene, polyaniline, polypyrrole, polythiophene and
polysulfur nitride.
10. The flexible secondary battery according to claim 1, wherein
when the battery is bent, the first electrode and the second
electrode move within the same bending radius.
11. The flexible secondary battery according to claim 1, wherein
the battery does not include an additional separator or electrolyte
layer between the first electrode and the second electrode.
12. The flexible secondary battery according to claim 1, further
comprising a cover member surrounding an exterior of the third
insulation coating layer.
13. The flexible secondary battery according to claim 12, wherein
the cover member comprises PVC, HDPE or epoxy resin.
14. The flexible secondary battery according to claim 1, wherein
the polyolefin foam separator of each of the first insulation
coating layer, the second insulation coating layer, and the third
insulation coating layer is formed by applying a coating solution
containing a foaming agent in a liquid phase of polyolefin to an
exterior of an electrode active material layer, followed by drying
and foaming.
15. The flexible secondary battery according to claim 1, wherein a
cross-section of the third insulation coating layer is a
peanut-like shape.
16. A flexible secondary battery comprising: a first electrode
comprising a first electrode current collector extended
longitudinally, a first electrode active material layer formed on
an outside of the first electrode current collector, and a first
insulation coating layer formed on an outside of the first
electrode active material layer; and a second electrode comprising
a second electrode current collector extended longitudinally, a
second electrode active material layer formed on an outside of the
second electrode current collector, and a second insulation coating
layer formed on an outside of the second electrode active material
layer, wherein the first electrode and the second electrode are
wound into parallel spring shapes of the same circumference that
are in contact with each other, wherein the flexible secondary
battery further comprises a third insulation coating layer
completely surrounding outside surfaces of both the first electrode
and the second electrode, and wherein the third insulation coating
layer is a helically wound structure in contact with the first
electrode and the second electrode so that the first electrode and
the second electrode are not spaced apart from each other even
under continuous bending of the secondary battery and are
maintained as one pair at an originally aligned position, wherein
the first electrode and the second electrode on which the third
insulating coating layer is formed are wound in a helical shape,
and the first and second electrodes contact each other on one side
only, whereas the other sides are spaced by the third insulating
coating layer.
17. A flexible secondary battery comprising: a first electrode
comprising a first electrode current collector extended
longitudinally, a first electrode active material layer formed on
an outside of the first electrode current collector, and a first
insulation coating layer formed on an outside of the first
electrode active material layer; and a second electrode comprising
a second electrode current collector extended longitudinally, a
second electrode active material layer formed on an outside of the
second electrode current collector, and a second insulation coating
layer formed on an outside of the second electrode active material
layer, wherein the first electrode and the second electrode are
helically wound in contact with each other such that they are
disposed alternately in parallel with each other on the same
circumference, wherein the flexible secondary battery further
comprises a third insulation coating layer completely surrounding
outside surfaces of both the first electrode and the second
electrode, and wherein the third insulation coating layer is a
helically wound structure in contact with the first electrode and
the second electrode so that the first electrode and the second
electrode are not spaced apart from each other even under
continuous bending of the secondary battery and are maintained as
one pair at an originally aligned position wherein each of the
first insulation coating layer, the second insulation coating
layer, and the third insulation coating layer comprises a
combination of oxide-based non-crosslinked polymer and polymer
crosslinked structure.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a national phase entry under 35 U.S.C.
.sctn. 371 of International Application No. PCT/KR2017/014489,
filed Dec. 11, 2017, published in Korean, which claims priority to
Korean Patent Application No. 10-2016-0167907, filed Dec. 9, 2016
in the Republic of Korea, the disclosures of which are incorporated
herein by reference.
TECHNICAL FIELD
The present disclosure relates to a flexible secondary battery.
More particularly, the present disclosure relates to a flexible
secondary battery which is freely deformable and has improved
flexibility.
BACKGROUND ART
Recently, development of wireless communication technology leads
popularization of mobile devices. In response to such development
of wireless technology, there is a strong tendency to use secondary
batteries essentially as power sources for devices. Meanwhile, with
a view to prevention of environmental pollution, electric vehicles
and hybrid vehicles have been developed and secondary batteries
have been used as power sources for such vehicles.
Thus, secondary batteries have been increasingly in use in various
industrial fields. Depending on characteristics of applications,
secondary batteries have been diversified in terms of output,
capacity and structure.
In general, a secondary battery includes an electrode assembly
obtained by applying an active material to the surface of a
plate-like current collector to form a cathode and an anode and
interposing a separator between the cathode and the anode. The
electrode assembly is received generally in a cylindrical or
prismatic metallic can or a pouch type casing including an aluminum
sheet together with a liquid electrolyte or solid electrolyte. In
addition, the electrode assembly may have a jelly-roll shape in
which sheet-type cathodes/separators/anodes are wound, or a
structure in which a plurality of unit electrodes having a thin
plate shape are stacked successively. Therefore, the structure of
an electrode (cathode and anode) in the electrode assembly
essentially has a plate-like shape.
Such a plate-like electrode structure is advantageous in that it
can realize a high degree of integration upon winding or stacking
of an electrode assembly. However, it has a limitation in
structural deformation depending on needs in industrial fields. In
addition, such a plate-like electrode structure has some problems,
since it is sensitive to a change in volume of an electrode during
charging/discharging, does not allow easy emission of gases
generated in a cell toward the outside, and may cause a large
difference in potential from one electrode to another
electrode.
Particularly, in response to various demands of consumers, devices
using a secondary battery have been diversified and designs of such
devices have become important. Contrary to this, it is required to
provide a separate site or space where a secondary battery having a
classical structure and/or shape (cylindrical, prismatic or pouch
shape) is installed for devices having a specific shape. This may
be a significant disadvantage in terms of extension of wireless
technology or limitation in designs. For example, when a space
configured to install a secondary battery is narrow and elongated
in a newly developed device, it is not possible or efficient to
install a secondary battery including such a conventional electrode
assembly based on a plate-like electrode after it is deformed
structurally. In other words, since a cylindrical battery, coin
battery or prismatic battery has a specific shape, it is not freely
deformable, has a limitation in use, and is not amenable to free
deformation, such as distortion or bending, in response to the
purpose of use a battery.
DISCLOSURE
Technical Problem
The present disclosure is designed to solve the problems of the
related art, and therefore the present disclosure is directed to
providing a flexible secondary battery which is easily deformable
and has an improved structure so as to maintain the stability and
high performance of a second battery.
Technical Solution
In one aspect of the present disclosure, there is provided the
flexible batteries according to the following embodiments.
According to a first embodiment of the present disclosure, there is
provided a flexible secondary battery which includes:
a first electrode including a first electrode current collector
extended longitudinally, a first electrode active material layer
formed on an outside of the first electrode current collector, and
a first insulation coating layer formed on an outside of the first
electrode active material layer; and
a second electrode including a second electrode current collector
extended longitudinally, a second electrode active material layer
formed on an outside of the second electrode current collector, and
a second insulation coating layer formed on an outside of the
second electrode active material layer,
wherein the first electrode and the second electrode are helically
wound in contact with each other such that they are disposed
alternately in parallel with each other on the same
circumference.
According to a second embodiment of the present disclosure, there
is provided the flexible secondary battery of the first embodiment,
wherein each of the first electrode current collector and the
second electrode current collector independently includes:
stainless steel; aluminum; nickel; titanium; baked carbon; copper;
stainless steel surface-treated with carbon, nickel, titanium or
silver; aluminum-cadmium alloy; non-conductive polymer
surface-treated with a conductive material; conductive polymer;
metal paste containing metal powder of Ni, Al, Au, Ag, Al, Pd/Ag,
Cr, Ta, Cu, Ba or ITO; or carbon paste containing carbon powder of
graphite, carbon black or carbon nanotube.
According to a third embodiment of the present disclosure, there is
provided the flexible secondary battery of the first or the second
embodiment, wherein the first electrode is a cathode or anode and
the second electrode is an anode or cathode corresponding to the
first electrode.
According to a fourth embodiment of the present disclosure, there
is provided the flexible secondary battery of any one of the first
to the third embodiments, wherein when the first electrode is an
anode and the second electrode is a cathode, the first electrode
active material includes any one active material particle selected
from the group consisting of natural graphite, artificial graphite
or carbonaceous materials; metals (Me) of lithium-containing
titanium composite oxide (LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or
Fe; alloys including the metal (Me); oxides (MeOx) of the metals
(Me); and composites of the metals (Me) with carbon, or a
combination of two or more of them, and
the second electrode active material includes any one active
material particle selected from the group consisting of
LiCoO.sub.2, LiNiO.sub.2, LiMn.sub.2O.sub.4, LiCoPO.sub.4,
LiFePO.sub.4, LiNiMnCoO.sub.2 and
LiNi.sub.1-x-y-zCo.sub.xM1.sub.yM2.sub.zO.sub.2 (wherein each of M1
and M2 independently represents any one selected from the group
consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, each
of x, y and z independently represents the atomic fraction of an
element forming the oxide and 0.ltoreq.x<0.5, 0.ltoreq.y<0.5,
0.ltoreq.z<0.5 and 0<x+y+z.ltoreq.1), or a combination of two
or more of them.
According to a fifth embodiment of the present disclosure, there is
provided the flexible secondary battery of any one of the first to
the fourth embodiments, wherein when the first electrode is a
cathode and the second electrode is an anode, the first electrode
active material includes any one active material particle selected
from the group consisting of LiCoO.sub.2, LiNiO.sub.2,
LiMn.sub.2O.sub.4, LiCoPO.sub.4, LiFePO.sub.4, LiNiMnCoO.sub.2 and
LiNi.sub.1-x-y-zCo.sub.xM1.sub.yM2.sub.zO.sub.2 (wherein each of M1
and M2 independently represents any one selected from the group
consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, each
of x, y and z independently represents the atomic fraction of an
element forming the oxide and 0.ltoreq.x<0.5, 0.ltoreq.y<0.5,
0.ltoreq.z<0.5 and 0<x+y+z.ltoreq.1), or a combination of two
or more of them, and
the second electrode active material includes any one active
material particle selected from the group consisting of natural
graphite, artificial graphite or carbonaceous materials; metals
(Me) of lithium-containing titanium composite oxide (LTO), Si, Sn,
Li, Zn, Mg, Cd, Ce, Ni or Fe; alloys including the metal (Me);
oxides (MeOx) of the metals (Me); and composites of the metals (Me)
with carbon, or a combination of two or more of them.
According to a sixth embodiment of the present disclosure, there is
provided the flexible secondary battery of any one of the first to
the fifth embodiments, wherein each of the first insulation coating
layer and the second insulation coating layer independently
includes a porous polymer coating layer; an inorganic solid-state
electrolyte coating layer; an organic solid-state coating layer; or
a polyolefin foam separator.
According to a seventh embodiment of the present disclosure, there
is provided the flexible secondary battery of any one of the first
to the sixth embodiments, which includes a third insulation coating
layer surrounding both the first electrode and the second
electrode.
According to an eighth embodiment of the present disclosure, there
is provided the flexible secondary battery of any one of the first
to the seventh embodiments, wherein the third insulation coating
layer includes a porous polymer coating layer; an inorganic
solid-state electrolyte coating layer; an organic solid-state
coating layer; or a polyolefin foam separator.
Advantageous Effects
The flexible secondary battery according to an embodiment of the
present disclosure includes the first electrode and the second
electrode, which have a longitudinally extended shape and are
disposed alternately in contact with each other, and thus can
improve the flexibility of the battery. Therefore, it is possible
to reduce the risk of a short-circuit caused by deformation, unlike
a foil type electrode which may form a sharp portion by deformation
to cause a short-circuit.
In addition, since the electrodes wound in the flexible secondary
battery according to an embodiment of the present disclosure are
easily deformable, the force applied to the electrode active
material layers may be dispersed, thereby contributing to
prevention of the separation of an active material layer from a
current collector.
DESCRIPTION OF DRAWINGS
The accompanying drawings illustrate a preferred embodiment of the
present disclosure and together with the foregoing disclosure,
serve to provide further understanding of the technical features of
the present disclosure, and thus, the present disclosure is not
construed as being limited to the drawing.
FIG. 1 is a schematic view illustrating the electrode according to
an embodiment of the present disclosure.
FIG. 2 is a schematic view illustrating the flexible secondary
battery including two electrodes according to an embodiment of the
present disclosure, before it is manufactured.
FIG. 3 is a schematic view illustrating the flexible secondary
battery according to an embodiment of the present disclosure.
FIG. 4 is a schematic view illustrating the flexible secondary
battery according to another embodiment of the present
disclosure.
FIG. 5 is a schematic view illustrating the flexible secondary
battery according to still another embodiment of the present
disclosure.
FIG. 6 is a schematic view illustrating the flexible secondary
battery according to still another embodiment of the present
disclosure.
FIG. 7 is a schematic view illustrating the flexible secondary
battery according to still another embodiment of the present
disclosure.
FIG. 8 is a schematic view illustrating the flexible secondary
battery according to still another embodiment of the present
disclosure.
FIG. 9 is a schematic view illustrating the flexible secondary
battery according to yet another embodiment of the present
disclosure.
FIG. 10 is a schematic view illustrating an extruder.
FIG. 11 shows extrusion coating of a wire shape using an O-die.
BEST MODE
Hereinafter, the present disclosure will be described in detail
with reference to the accompanying drawings. It should be
understood that the constitution shown in the drawings is just a
preferable example for the purpose of illustrations only, not
intended to limit the scope of the disclosure, so it should be
understood that other equivalents and modifications could be made
thereto without departing from the scope of the disclosure.
The flexible secondary battery according to an embodiment of the
present disclosure includes: a first electrode including a first
electrode current collector extended longitudinally, a first
electrode active material layer formed on an outside of the first
electrode current collector, and a first insulation coating layer
formed on an outside of the first electrode active material layer;
and a second electrode including a second electrode current
collector extended longitudinally, a second electrode active
material layer formed on an outside of the second electrode current
collector, and a second insulation coating layer formed on an
outside of the second electrode active material layer, wherein the
first electrode and the second electrode are helically wound in
contact with each other such that they are disposed alternately in
parallel with each other on the same circumference.
Referring to FIG. 1, each of the electrodes (the first electrode
and the second electrode) in the flexible secondary battery
according to the present disclosure is provided with an electrode
current collector 21 extended longitudinally, an electrode active
material layer 22 formed on the outside of the electrode current
collector 21, and an insulation coating layer 23 formed on the
outside of the first electrode active material layer 22.
Referring to FIG. 2 and FIG. 3, a first electrode 30 including a
first electrode current collector 31 extended longitudinally, a
first electrode active material layer 32 formed on the outside of
the first electrode current collector 31, and a first insulation
coating layer 33 formed on the outside of the first electrode
active material layer 32; and a second electrode 40 including a
second electrode current collector 41 extended longitudinally, a
second electrode active material layer 42 formed on the outside of
the second electrode current collector 41, and a second insulation
coating layer 43 formed on the outside of the second electrode
active material layer 42 are prepared, and then the first electrode
30, 110 and the second electrode 40, 120 are wound so that they may
be disposed alternately in contact with each other. In this manner,
it is possible to form the flexible secondary battery 100 according
to the present disclosure.
In the flexible secondary battery according to the present
disclosure, the first electrode and the second electrode are
extended longitudinally, and have a structure in which they are
wound spirally so that they are disposed alternately in contact
with each other. Herein, the term `spiral` may be interchanged with
`helix`, means a shape which winds diagonally in a certain range,
and generally refers to a shape similar to the shape of a general
spring.
In the flexible secondary battery according to the present
disclosure, it does not have a concentric circular shape in which
one of the first electrode and the second electrode is disposed at
the inside and the other is disposed at the outside so that one
electrode is surrounded with the other electrode present at the
outside, but has a shape in which the first electrode and the
second electrode are aligned alternately in parallel with each
other on the same circumference.
In the battery structure including an internal electrode and an
external electrode surrounding the same according to the related
art, a separator layer (separator, electrolyte layer, etc.) is
disposed between the internal electrode and the external electrode
in order to impart insulation property between both electrodes.
However, a space is present while the external electrode surrounds
the internal electrode. Particularly, when bending is repeated
under the application of external force to the battery, the
internal electrode and the external electrode show a different
range of extension/shrinking due to their different bending radii,
friction occurs while they are spaced apart from each other to
release stress, and the separator may be damaged or the electrode
active material may be separated, resulting in generation of a
short-circuit undesirably between the electrodes at such a spaced
portion.
In addition, in the case of a battery including a first electrode
structure having a linear or spiral shape and a second electrode
structure surrounding the outside of the first electrode structure
according to the related art, flexibility is degraded due to the
portion where the first electrode structure and the second
electrode structure are in contact with each other while the former
is surrounded with the latter. In addition, while bending occurs
repeatedly, the portion impairs the separator due to the friction
of the portion or damages the electrode structures due to the
separation of the electrode active material.
On the contrary, in the flexible secondary battery according to the
present disclosure, the surfaces (winding surfaces) on which the
first electrode and the second electrode are wound are disposed on
the same circumferential surface, and thus the electrodes move
within the same bending radius upon the bending of the battery,
thereby preventing stimulation in the vertical direction. In
addition, since the first electrode and the second electrode of the
flexible secondary battery according to the present disclosure are
disposed in contact with each other, flexibility is improved
significantly, thereby preventing the insulation coating layers
from being damaged by the friction of the first insulating layer
and the second insulating layer, even when the battery is subjected
to bending repeatedly. Therefore, it is possible to prevent
short-circuit between electrodes, which occurs in the
above-mentioned battery structures according to the related
art.
The cross-section of the first electrode current collector and that
of the second electrode current collector are not particularly
limited but may have a circular, ellipsoidal or polygonal shape,
and particular examples of the polygonal shape may include a
triangular, quadrangular or hexagonal shape.
Each of the first electrode current collector and the second
electrode current collector may be prepared preferably by using
stainless steel, aluminum, nickel, titanium, baked carbon, copper,
stainless steel surface-treated with carbon, nickel, titanium or
silver, aluminum-cadmium alloy, a non-conductive polymer
surface-treated with a conductive material, or a conductive
polymer.
The current collector functions to collect the electrons generated
by the electrochemical reaction of an electrode active material or
to supply the electrons required for electrochemical reaction. In
general, a metal, such as copper or aluminum is used as a current
collector. Particularly, when using a polymer conductor including a
conductive polymer or a non-conductive polymer surface-treated with
a conductive material, it is possible to obtain relatively higher
flexibility as compared to a metal such as copper or aluminum. In
addition, it is possible to accomplish the weight lightening of a
battery by using a polymer current collector instead of a metal
current collector.
Conductive materials that may be used include polyacetylene,
polyaniline, polypyrrole, polythiophene, polysulfur nitride, indium
tin oxide (ITO), copper, silver, palladium and nickel. Conductive
polymers that may be used include polyacetylene, polyaniline,
polypyrrole, polythiophene and polysulfur nitride. However, the
non-conductive polymer used for a current collector is not
particularly limited.
The first electrode may be a cathode and the second electrode may
be an anode. Otherwise, the first electrode may be an anode and the
second electrode may be a cathode. Therefore, it is possible to
select a material for the first electrode active material layer or
the second electrode active material layer adequately depending on
the particular type of each electrode.
When the first electrode is an anode and the second electrode is a
cathode, the first electrode active material layer becomes an anode
active material layer, and non-limiting examples thereof include
natural graphite, artificial graphite or carbonaceous materials;
metals (Me) such as lithium-containing titanium composite oxide
(LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; alloys including the
metal (Me); oxides (MeOx) of the metals (Me); composites of the
metals (Me) with carbon; or the like. In addition, the second
electrode active material layer becomes a cathode active material
layer, and non-limiting examples thereof include LiCoO.sub.2,
LiNiO.sub.2, LiMn.sub.2O.sub.4, LiCoPO.sub.4, LiFePO.sub.4,
LiNiMnCoO.sub.2, LiNi.sub.1-x-y-zCo.sub.xM1.sub.yM2.sub.zO.sub.2
(wherein each of M1 and M2 independently represents any one
selected from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr,
Ti, W, Ta, Mg and Mo, each of x, y and z independently represents
the atomic fraction of an element forming the oxide and
0.ltoreq.x<0.5, 0.ltoreq.y<0.5, 0.ltoreq.z<0.5 and
0<x+y+z.ltoreq.1), or the like.
In addition, when the first electrode is a cathode and the second
electrode is an anode, the first electrode active material layer
becomes a cathode active material layer and the second electrode
active material layer becomes an anode active material layer.
The electrode active material layer further includes a binder and a
conductive material, besides the electrode active materials, and
may be bound with the current collector to form an electrode. Such
a binder allows binding of the electrode active material to the
current collector to prevent separation, when the electrode is
deformed by folding or severe bending due to external force.
The conductive material may include any one selected from the group
consisting of carbon black, acetylene black, Ketjen black, carbon
fiber, carbon nanotube and graphene, or a combination of two or
more of them, but is not limited thereto.
The binder may be any one selected from the group consisting of
polyvinylidene fluoride (PVDF), polyvinylidene
fluoride-co-hexafluoropropylene, polyvinylidene
fluoride-co-trichloroethylene, polybutyl acrylate, polymethyl
methacrylate, polyacrylonitrile, polyvinylpyrrolidone,
polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene
oxide, polyarylate, cellulose acetate, cellulose acetate butyrate,
cellulose acetate propionate, cyanoethylpullulan,
cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose,
pullulan, carboxymethyl cellulose, styrene-butadiene rubber,
acrylonitrile-styrene-butadiene copolymer and polyimide, or a
combination thereof, but is not limited thereto.
In addition, each of the first electrode and the second electrode
of the flexible secondary battery according to the present
disclosure is provided with an insulation coating layer (first
insulation coating layer, second insulation coating layer) at the
outside of each electrode active material layer.
The insulation coating layer functions as an electrical insulation
layer which prevents a short-circuit between the first electrode
and the second electrode even when both electrodes are disposed
alternately in contact with each other, as well as functions to
form a channel through which lithium ions can be transported
between both electrodes.
Further, the insulation coating layer functions as a protective
coating layer which prevents separation of the active material of
the active material layer by imparting flexibility to the
electrode, even when the electrode is bent severely.
As a result, in the flexible secondary battery according to the
present disclosure, it is possible to eliminate a separator layer
(separator or electrolyte), which, otherwise, should be interposed
between an internal electrode and an external electrode in the
conventional battery having a structure of an internal electrode
and an external electrode surrounding the same.
In addition, the flexible secondary battery according to the
present disclosure is freely deformable and has a certain degree of
elasticity by virtue of the presence of such insulation coating
layers, and thus has excellent flexibility. Further, while a
currently used foil type electrode forms a sharp portion by
deformation and the portion may infiltrate into an electrolyte
layer to cause a short-circuit, the flexible secondary battery
according to the present disclosure is not easily folded or bent
and is not susceptible to formation of a sharp portion upon
deformation to prevent the problem of a short-circuit.
According to an embodiment of the present disclosure, each of the
first insulation coating layer and the second insulation coating
layer independently includes a porous polymer coating layer;
inorganic solid-state electrolyte coating layer; organic
solid-state coating layer; or a polyolefin foam separator.
The porous polymer coating layer is a polymer film having pores
formed by a phase separation of a polymer, and particular examples
of the polymer include polyvinylidene fluoride (PVDF),
polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene
fluoride-co-trichloroethylene, or the like.
The inorganic solid-state coating layer is a coating layer formed
by applying a solid electrolyte composition including an inorganic
solid electrolyte and a polymer binder. The inorganic solid
electrolyte includes a metal that belongs to Group 1 or Group 2 in
the Periodic Table, and generally has metal ion (preferably,
lithium ion) conductivity but has no electron conductivity.
According to an embodiment of the present disclosure, the inorganic
solid electrolyte may be selected from the solid electrolyte
materials applied to solid-state secondary batteries, and
particular examples of the solid electrolyte materials include a
sulfide-based inorganic solid electrolyte, oxide-based inorganic
solid electrolyte, or the like.
The sulfide-based inorganic solid electrolyte preferably contains
sulfur (S), includes a metal that belongs to Group 1 or Group 2 in
the Periodic Table, and has ion conductivity and electron
insulating property. For example, a lithium ion conductive
inorganic solid electrolyte satisfying the composition represented
by the following Chemical Formula 1 may be used.
Li.sub.aM.sub.bP.sub.cS.sub.d (1) wherein M represents an element
selected from B, Zn, Si, Cu, Ga and Ge. Each of a-d represents the
compositional ratio of each element, wherein a:b:c:d satisfies
1-12: 0-0.2:1:2-9.
In Chemical Formula 1, the compositional ratio of Li, M, P and S
preferably satisfies b=0. More preferably, b=0 and the
compositional ratio of a, c and d satisfies a:c:d=1-9:1:3-7. Even
more preferably, b=0 and a:c:d=1.5-4:1:3.25-4.5. As described
hereinafter, the compositional ratio of each element may be
controlled by adjusting the mixing amount of a starting compound
when preparing the sulfide-based solid electrolyte.
The sulfide-based inorganic solid electrolyte may be amorphous
(vitreous), may be in a crystallized form (vitreous ceramic), or
may be in a partially crystallized form. In Li--P--S type glass and
Li--P--S type vitreous ceramic, the ratio of Li.sub.2S to
P.sub.2S.sub.5 is the molar ratio of Li.sub.2S:P.sub.2O.sub.5 and
may be preferably 65: 35-85:15, more preferably 68: 32-75:25. When
the ratio of Li.sub.2S to P.sub.2S.sub.5 is within the
above-defined range, it is possible to obtain higher lithium ion
conductivity. The lithium ion conductivity may be preferably
1.times.10.sup.-4 S/cm or more, more preferably 1.times.10.sup.-3
S/cm or more. Particular examples of such compounds include one
obtained by using a composition containing sulfide of an element of
Group 13-Group 15.
Particular examples of the sulfide-based inorganic solid
electrolyte include Li.sub.2S--P.sub.2S.sub.5,
Li.sub.2S--GeS.sub.2, Li.sub.2S--GeS.sub.2--ZnS,
Li.sub.2S--Ga.sub.2S.sub.3, Li.sub.2S--GeS.sub.2--Ga.sub.2S.sub.3,
Li.sub.2S--GeS.sub.2--P.sub.2S.sub.5,
Li.sub.2S--GeS.sub.2--Sb.sub.2S.sub.5,
Li.sub.2S--GeS.sub.2--Al.sub.2S.sub.3, Li.sub.2S--SiS.sub.2,
Li.sub.2S--Al.sub.2S.sub.3, Li.sub.2S--SiS.sub.2--Al.sub.2S.sub.3,
Li.sub.2S--SiS.sub.2--P.sub.2S.sub.5, Li.sub.2S--SiS.sub.2--LiI,
Li.sub.2S--SiS.sub.2--Li.sub.4SiO.sub.4,
Li.sub.2S--SiS.sub.2--Li.sub.3PO.sub.4, Li.sub.10GeP.sub.2S.sub.12,
or the like. Particularly, a crystalline and/or amorphous
composition including Li.sub.2S--P.sub.2S.sub.5,
Li.sub.2S--GeS.sub.2--Ga.sub.2S.sub.3,
Li.sub.2S--GeS.sub.2--P.sub.2S.sub.5,
Li.sub.2S--SiS.sub.2--P.sub.2S.sub.5,
Li.sub.2S--SiS.sub.2--Li.sub.4SiO.sub.4 or
Li.sub.2S--SiS.sub.2--Li.sub.3PO.sub.4 is preferred, since it has
high lithium ion conductivity.
Particular examples of the method for preparing a sulfide-based
solid electrolyte material by using the above-mentioned
compositions include amorphization. For example, such amorphization
may include a mechanical milling process and a melt quenching
process. Among them, a mechanical milling process is preferred,
since it allows treatment at room temperature, and thus simplifies
the preparation process.
The oxide-based inorganic solid electrolyte contains an oxygen atom
(O), includes a metal that belongs to Group 1 or Group 2 in the
Periodic Table, and preferably has ion conductivity and electron
insulating property.
Particular examples of the oxide-based inorganic solid electrolyte
include Li.sub.xaLa.sub.yaTiO.sub.3 [xa=0.3-0.7, ya=0.3-0.7] (LLT),
Li.sub.7La.sub.3Zr.sub.2O.sub.12(LLZ),
Li.sub.3.5Zn.sub.0.25GeO.sub.4 having a LISICON (lithium super
ionic conductor)-type crystal structure, LiTi.sub.2P.sub.3O.sub.12
having a NASICON (natrium super ionic conductor)-type crystal
structure,
Li.sub.a+xb+yb(Al,Ga).sub.xb(Ti,Ge).sub.2-xbSi.sub.ybP.sub.3-ybO.sub.12
(wherein 0.ltoreq.xb.ltoreq.1, 0.ltoreq.yb.ltoreq.1),
Li.sub.7La.sub.3Zr.sub.2O.sub.12 having a garnet-type crystal
structure.
In addition, a phosphorus-based compound containing Li, P and O is
preferred and particular examples thereof include LiPON, LiPOD
(wherein D is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni,
Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc.). In addition, LiAON
(wherein A is Si, B, Ge, Al, C, Ga, etc.) may be used
preferably.
Particularly,
Li.sub.1+xb+yb(Al,Ga).sub.xb(Ti,Ge).sub.2-xbSi.sub.ybP.sub.3-ybO.sub.12
(wherein 0.ltoreq.xb.ltoreq.1, 0.ltoreq.yb.ltoreq.1) is preferred,
since it has high lithium ion conductivity, is chemically stable
and can be handled with ease. Such compounds may be used alone or
in combination.
The oxide-based solid electrolyte preferably has a lithium ion
conductivity of 1.times.10.sup.-6 S/cm or more, more preferably
1.times.10.sup.-5 S/cm or more, and most preferably
5.times.10.sup.-5 S/cm or more.
Binder polymers that may be used in the inorganic solid-state
electrolyte coating layer include amide bond-containing polymers,
such as polyamide and polyacrylamide; imide bond-containing
polymers such as polyimide; urethane bond-containing polymers such
as polyurethane; rubber such as nitrile butadiene rubber (NBR),
butadiene rubber and butylene rubber; polyacrylates;
poly(styrene-butadiene-styrene); or the like.
In addition, the organic solid-state coating layer may include a
polar non-crosslinked polymer, oxide-based non-crosslinked polymer,
polymer crosslinked structure, or a combination of two or more of
them.
Particular examples of the polar non-crosslinked polymers may
include, but are not limited to: polyvinyl chloride, polyvinylidene
fluoride, polyvinylidene fluoride-co-hexafluoropropylene,
polyethylene imine, polymethacrylate, polybutyl acrylate, polyvinyl
alcohol, polyvinyl pyrrolidone, polyvinyl acetate,
ethylene-co-vinyl acetate, phosphate polymers, polyagitation
lysine, polymers containing an ionically dissociatable group, or a
combination of two or more of them.
The oxide-based non-crosslinked polymers include polyethylene
oxide, polypropylene oxide, polyoxymethylene, polydimethyl
siloxane, polyethylene sulfide, derivatives thereof, or a
combination of two or more of them, but are not limited
thereto.
The polymer crosslinked structures include polymers of a monomer
having two or more functional groups or copolymers of a monomer
having two or more functional groups with a polymer monomer having
one functional group.
Particular examples of the monomer having two or more functional
groups include, but are not limited to: trimethylolpropane
ethoxylate triacrylate, polyethylene glycol dimethacrylate,
polyethylene glycol diacrylate, divinyl benzene, polyester
dimethacrylate, divinyl ether, trimethylolpropane,
trimethylolpropane trimethacrylate, ethoxylated bisphenol A
dimethacrylate, or a combination of two or more of them.
Particular examples of the monomer having one functional group
include, but are not limited to: methyl methacrylate, ethyl
methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate,
ethylene glycol methyl ether acrylate, ethylene glycol methyl ether
methacrylate, acrylonitrile, vinyl acetate, vinyl chloride, vinyl
fluoride, or a combination of two or more of them.
The polyolefin foam separator may be formed by applying a coating
solution containing a foaming agent in a liquid phase of polyolefin
to the exterior of an electrode active material layer, followed by
drying and foaming, to obtain a foam separator layer. The
polyolefin may include polyethylene, polypropylene, or the like.
The foaming agent may include at least one selected from the group
consisting of azo (--N.dbd.N--) compounds, carbonate compounds,
hydrazide compounds, nitrile compounds, amine compounds, amide
compounds and carbazide compounds.
According to the present disclosure, the insulation coating layer
may further include a lithium salt. Such a lithium salt can improve
ion conductivity and reaction rate, and particular examples thereof
include LiCl, LiBr, LiI, LiClO.sub.4, LiBF.sub.4,
LiB.sub.10Cl.sub.10, LiPF.sub.6, LiCF.sub.3SO.sub.3,
LiCF.sub.3CO.sub.2, LiAsF.sub.6, LiSbF.sub.6, LiAlCl.sub.4,
CH.sub.3SO.sub.3Li, CF.sub.3SO.sub.3Li,
(CF.sub.3SO.sub.2).sub.2NLi, (FSO.sub.2).sub.2NLi, lithium
chloroborate, lower aliphatic lithium carboxylate and lithium
tetraphenylborate.
Referring to FIG. 4, the flexible secondary battery according to
the present disclosure is provided with a first electrode 200
including a first electrode current collector 210 extended
longitudinally, a first electrode active material layer 220 formed
on the outside of the first electrode current collector, and a
first insulation coating layer 230 formed on the outside of the
first electrode active material layer; and a second electrode 300
including a second electrode current collector 310 extended
longitudinally, a second electrode active material layer 320 formed
on the outside of the second electrode current collector, and a
second insulation coating layer 330 formed on the outside of the
second electrode active material layer, wherein the first electrode
and the second electrode are wound in such a manner that they are
disposed alternately in contact with each other. The flexible
secondary battery may be provided with a cover member 400 which
surrounds the outside of the first electrode and the second
electrode.
The cover member is an insulator and is formed to surround the
electrode assembly in order to protect the electrodes from moisture
in the air and external impact. The cover member may include a
conventional polymer resin and particular examples thereof include
PVC, HDPE or epoxy resin.
According to an embodiment of the present disclosure, the flexible
secondary battery may be further provided with a third insulation
coating layer which surrounds both the first electrode and the
second electrode. In the same manner as the first insulation
coating layer and the second insulation coating layer, the third
insulation coating layer may include the porous polymer coating
layer, inorganic solid-state electrolyte coating layer, organic
solid-state coating layer, or the polyolefin foam separator as
described above.
According to the flexible secondary battery provided with the third
insulation coating layer, the first electrode and the second
electrode are not spaced apart from each other even under
continuous bending of the secondary battery, and are maintained as
one pair at the originally aligned position, as compared to a
flexible secondary battery including a first electrode and a second
electrode adjacent thereto and having no insulation coating layer
surrounding the electrodes. As a result, it is possible to inhibit
the first electrode and the second electrode from being spaced
apart from each other due to bending, to prevent the insulation
coating layers from being damaged by friction between the first
insulation coating layer and the second insulation coating layer
provided on the outside of the first electrode and the second
electrode, and to prevent a short-circuit between the first
electrode and the second electrode.
Referring to FIG. 5-FIG. 8, a first electrode 30 including a first
electrode current collector 31 extended longitudinally, a first
electrode active material layer 32 formed on the outside of the
first electrode current collector 31, and a first insulation
coating layer 33 formed on the outside of the first electrode
active material layer 32; and a second electrode 40 including a
second electrode current collector 41 extended longitudinally, a
second electrode active material layer 42 formed on the outside of
the second electrode current collector 41, and a second insulation
coating layer 43 formed on the outside of the second electrode
active material layer 42 are prepared, the first electrode 30, 110
and the second electrode 40, 120 are disposed with a predetermined
interval, and then a third insulation coating layer 50, 130
surrounding both electrodes is formed. Then, the first electrode
30, 110 and the second electrode 40, 120 are wound spirally to form
the flexible secondary battery 100 shown in FIG. 8, in which the
first electrode 30, 110 and the second electrode 40, 120 are
disposed alternately according to an embodiment of the present
disclosure.
Particularly, referring to FIG. 5-FIG. 7, the cross-section of the
third insulation coating layer 50, 130 may be an elliptical (FIG.
5), rectangular (FIG. 6) or peanut-like shape (FIG. 7) and other
shapes, such as a circular shape, square shape or various polygonal
shapes including a triangular shape may be used.
Referring to FIG. 9, the flexible secondary battery may be further
provided with a cover member 400 surrounding the exterior of the
third insulation coating layer 50, 130.
Hereinafter, the method for manufacturing the flexible secondary
battery as described above will be explained.
First, an active material layer is formed on the surface of a first
electrode current collector having an elongated wire shape whose
cross-section perpendicular to the longitudinal direction has a
circular, elliptical or a polygonal shape.
Any conventional coating processes may be used for forming the
first electrode active material layer. Particularly, it is
preferred to form the first electrode active material layer by
using a continuous or discontinuous extrusion coating process in
which electrode slurry containing an active material is passed
through an extruder. Herein, the active material layer may be
coated intermittently so as to maintain a predetermined
interval.
Next, a first insulation coating layer is formed to surround the
first electrode active material layer.
There is no particular limitation in methods for forming the first
insulation coating layer. The first insulation coating layer may be
applied through various processes applicable in the art by using an
insulation coating layer composition (coating solution) containing
materials for forming the insulation coating layer. For example, it
is possible to use a dip coating or extrusion coating process.
Considering the characteristics of a linear flexible secondary
battery, an extrusion coating process facilitates manufacture of
the battery.
For example, in the case of the extrusion coating process, it
performs coating continuously by extruding a coating solution onto
the outer surface of a substrate through an extruder, and thus has
little limitation in length of the substrate to be coated and
allows continuous coating on a substrate having a uniform shape.
Referring to FIG. 10, the extruder generally includes a hopper 1,
cylinder 2 and a die 5. A general extrusion coating process
includes introducing a coating material to the hopper of the
extruder, allowing the cylinder to maintain a predetermined
temperature, and rotating the screw 3 in the cylinder 2, while the
coating material is molten, to push out the coating solution and to
allow the coating solution to pass through the die 5 mounted in
front of the cylinder so that it may be coated on the substrate.
The flexible secondary battery has a characteristic shape in that
it is elongated in the longitudinal direction as compared to its
horizontal section and has a desired horizontal section. Thus, it
is suitable to apply a continuous coating process based on
extrusion coating.
The electrode slurry is introduced to the hopper 1 of the extruder
and the screw 3 in the cylinder is rotated to perform mixing and to
push out the electrode slurry so that the electrode slurry may pass
through the die 5 mounted in front of the cylinder 2 and may be
extruded and coated onto the current collector supplied to the
extruder, thereby providing an electrode which is the first
electrode (anode or cathode) and the second electrode (cathode or
anode) extended longitudinally. The current collector for forming
the electrode may have a wire-like shape. The type of a die
depending on the shape of a current collector is not particularly
limited. However, when the current collector has a wire-like shape,
it may be passed through a pipe-like O-die (see FIG. 11) so that
the outer surface of the current collector may be coated with the
electrode slurry. The electrode slurry injected to the extruder is
supplied through a coating material supplying unit 11 and
discharged through the O-die 10. The discharged electrode slurry is
extrusion coated on the wire-like current collector 12 inserted
through the lateral surface of the O-die. Herein, it is possible to
control the thickness of the coating layer with ease by adjusting
the concentration of electrode slurry, extrusion rate or the line
speed (feed rate to the extruder) of the current collector.
Then, the second electrode provided with the second insulation
coating layer is prepared in the same manner as the method for
manufacturing the first electrode, except that an active material
for the electrode opposite to the electrode including the
above-mentioned active material layer is used. For example, each of
the first insulation coating layer and the second insulation
coating layer may have a thickness of 5-150 .mu.m.
After that, the first electrode and the second electrode are wound
spirally in the longitudinal direction while they are in contact
with each other to form an electrode assembly in which the first
electrode and the second electrode are disposed alternately on the
same circumferential surface.
Then, the obtained electrode assembly is surrounded with a cover
member to obtain a flexible secondary battery. The cover member is
an insulator and is formed on the outermost surface in order to
protect the battery from moisture in the air and external impact.
The cover member may include a conventional polymer resin and
particular examples thereof include polyvinyl chloride (PVC),
high-density polyethylene (HDPE) or epoxy resin.
According to an embodiment of the present disclosure, the flexible
secondary battery may be further provided with a third insulation
coating layer surrounding both the first electrode and the second
electrode. Herein, the third insulation coating layer may be formed
by forming two holes in the extruder as shown in FIG. 11 so that
two coating substrates may be introduced to the extruder,
introducing the first electrode and the second electrode to each of
the holes and introducing the third insulation coating layer
material as the coating material.
MODE FOR DISCLOSURE
Hereinafter, the present disclosure will be explained in detail
with reference to Examples. The following examples may, however, be
embodied in many different forms and should not be construed as
limited to the exemplary embodiments set forth therein. Rather,
these exemplary embodiments are provided so that the present
disclosure will be thorough and complete, and will fully convey the
scope of the present disclosure to those skilled in the art.
Example 1
A mixture of natural graphite/acetylene black/PVDF=70/5/25 was
mixed with N-methylpyrrolidone (NMP) as a solvent to obtain slurry
for an anode active material, which, in turn, was coated onto a
wire-like current collector made of copper and having a diameter of
125 .mu.m, thereby forming an anode active material layer.
A mixture of LiCoO.sub.2/acetylene black/PVDF=70/5/25 was mixed
with N-methylpyrrolidone (NMP) as a solvent to obtain slurry for a
cathode active material, which, in turn, was coated onto a
wire-like current collector made of aluminum and having a diameter
of 125 .mu.m, thereby forming a cathode active material layer.
Polyethylene oxide (PEO) (weight average molecular weight
(Mw)=4,000,000 g/mol) was dissolved in acetonitrile (AN) as a
solvent to prepare a 4 wt % PEO solution, and lithium
bis(fluorosulfonyl) imide (LiFSI, (FSO.sub.2).sub.2NLi) as a
lithium salt was added thereto to a molar ratio of
[EO]/[Li.sup.+]=20/1. Then, the resultant mixture was agitated over
night at 70.degree. C. so that PEO and lithium salt might be
dissolved sufficiently in the PEO solution.
In addition, in order to obtain a polymer crosslinked structure,
polyethylene glycol diacrylate (PEGDA) having two functional groups
(weight average molecular weight (Mw)=575) and benzoyl peroxide
(BPO) as an initiator were introduced to the lithium salt solution
and agitated sufficiently to prepare a composition for an
insulation coating layer. Herein, PEGDA was used in an amount of 20
parts by weight based on 100 parts by weight of PEO and BPO was
used in an amount of 1 part by weight based on 100 parts by weight
of PEGDA.
Then, the prepared composition for forming an insulation coating
layer was coated onto each of the anode active material layer and
the cathode active material layer. The coating was carried out
through extrusion coating.
Particularly, the composition for forming an insulation coating
layer was introduced to the hopper of an extruder. The cylinder of
the extruder was maintained at a temperature of 50.degree. C. and
the screw rotation speed was maintained at 60-70 rpm. The current
collector having the anode active material layer was supplied to
the O-die (see FIG. 11) of the extruder at a rate of 3 m/minute so
that the outer surface of the anode active material layer might be
extrusion coated with the composition for forming an insulation
coating layer. After that, the coating composition was dried in the
chamber of a dryer at 100.degree. C. and subjected to vacuum drying
at the same temperature for 12 hours to obtain an anode (first
electrode) provided with a first insulation coating layer. Herein,
the first insulation coating layer had a thickness of about 20
.mu.m.
The same method for manufacturing an anode as described above was
used to obtain a cathode (second electrode) having a second
insulation coating layer formed on the outer surface thereof,
except that the current collector having the cathode active
material layer was used.
Then, while the prepared anode and cathode were allowed to be in
contact with each other, they were wound spirally in the
longitudinal direction to form a spring-shaped electrode assembly
including the anode and the cathode disposed alternately on the
same circumferential surface. The obtained electrode assembly was
surrounded with a cover member made of polyvinyl chloride (PVC)
resin to obtain a flexible secondary battery.
Example 2
A mixture of natural graphite/acetylene black/PVDF=70/5/25 was
mixed with N-methylpyrrolidone (NMP) as a solvent to obtain slurry
for an anode active material, which, in turn, was coated onto a
wire-like current collector made of copper and having a diameter of
125 .mu.m, thereby forming an anode active material layer.
A mixture of LiCoO.sub.2/acetylene black/PVDF=70/5/25 was mixed
with N-methylpyrrolidone (NMP) as a solvent to obtain slurry for a
cathode active material, which, in turn, was coated onto a
wire-like current collector made of aluminum and having a diameter
of 125 .mu.m, thereby forming a cathode active material layer.
Polyethylene oxide (PEO) (weight average molecular weight
(Mw)=4,000,000 g/mol) was dissolved in acetonitrile (AN) as a
solvent to prepare a 4 wt % PEO solution, and lithium
bis(fluorosulfonyl) imide (LiFSI, (FSO.sub.2).sub.2NLi) as a
lithium salt was added thereto to a molar ratio of
[EO]/[Li.sup.+]=20/1. Then, the resultant mixture was agitated over
night at 70.degree. C. so that PEO and lithium salt might be
dissolved sufficiently in the PEO solution.
In addition, in order to obtain a polymer crosslinked structure,
polyethylene glycol diacrylate (PEGDA) having two functional groups
(weight average molecular weight (Mw)=575) and benzoyl peroxide
(BPO) as an initiator were introduced to the lithium salt solution
and agitated sufficiently to prepare a composition for an
insulation coating layer. Herein, PEGDA was used in an amount of 20
parts by weight based on 100 parts by weight of PEO and BPO was
used in an amount of 1 part by weight based on 100 parts by weight
of PEGDA.
Then, the prepared composition for forming an insulation coating
layer was coated onto each of the anode active material layer and
the cathode active material layer. The coating was carried out
through extrusion coating.
Particularly, the composition for forming an insulation coating
layer was introduced to the hopper of an extruder. The cylinder of
the extruder was maintained at a temperature of 50.degree. C. and
the screw rotation speed was maintained at 60-70 rpm. The current
collector having the anode active material layer was supplied to
the O-die (see FIG. 11) of the extruder at a rate of 3 m/minute so
that the outer surface of the anode active material layer might be
extrusion coated with the composition for forming an insulation
coating layer. After that, the coating composition was dried in the
chamber of a dryer at 100.degree. C. and subjected to vacuum drying
at the same temperature for 12 hours to obtain an anode (first
electrode) provided with a first insulation coating layer. Herein,
the first insulation coating layer had a thickness of about 20
.mu.m.
The same method for manufacturing an anode as described above was
used to obtain a cathode (second electrode) having a second
insulation coating layer formed on the outer surface thereof,
except that the current collector having the cathode active
material layer was used.
Then, while the prepared anode and cathode were disposed with a
predetermined interval, a third insulation coating layer
surrounding both the anode and the cathode was formed through
extrusion coating.
Particularly, the composition for forming an insulation coating
layer was introduced to the hopper of the extruder, the cylinder of
the extruder was maintained at a temperature of 50.degree. C. and
the screw rotation speed was maintained at 60-70 rpm. The anode and
the cathode was supplied to the O-die (see FIG. 11) of the extruder
having two holes (inlets) spaced apart from each other by a
predetermined distance at a rate of 3 m/minute so that the outer
surfaces of the anode and cathode might be extrusion coated totally
with the composition for forming an insulation coating layer. After
that, the coating composition was dried in the chamber of a dryer
at 100.degree. C. and subjected to vacuum drying at the same
temperature for 12 hours to form the third insulation coating layer
surrounding both the anode and the cathode.
Then, the anode and the cathode having the third insulation coating
layer were wound spirally together in the longitudinal direction to
form a spring-shaped electrode assembly including the anode and the
cathode disposed alternately on the same circumferential surface.
The obtained electrode assembly was surrounded with a cover member
made of polyvinyl chloride (PVC) resin to obtain a flexible
secondary battery.
* * * * *